This invention concerns brachytherapy, particularly for treatment of surrounding tissue after removal of a malignant tumor. In particular the invention concerns protection of adjacent healthy tissue such as skin, bone or organs that would otherwise be susceptible to being overdosed with radiation.
Local radiation therapy is often prescribed following breast surgery. Traditionally, this radiation is supplied by large machines positioned over the patient in extensively shielded special radiation therapy rooms from which casual observers or therapists must be excluded during treatment. Breast brachytherapy is a more recently developed medical procedure that involves delivering ionizing radiation to breast tissue from inside of a surgical cavity formed after a lumpectomy procedure. Breast brachytherapy is typically performed with a balloon catheter or other type of applicator positioned inside the cavity. The balloon or applicator fills the cavity and provides a platform or channel for introduction of radioactive material or a miniature x-ray tube. It also serves to locate the radiation source within the cavity such that the ionizing radiation sterilizes accurately treats the margins of the surgical cavity. Radiation treatment of surgical margins has been shown to reduce the rate of recurrence of malignant tissue.
Preparatory to a breast lumpectomy, the tumor has usually been located by any of several means known to medical practitioners. During lumpectomy, it is common practice to excise not only the tumor, but also a margin around the tumor, often a centimeter radially, to assure all diseased tissue is removed. To commence a lumpectomy procedure, the surgeon sharply dissects breast tissue toward the tumor to be excised. As he gets close to the tumor, he starts to cut around the lesion until the target tissue has been separated from the surrounding, presumed normal tissue. At this point, the tumor and excised margin are removed through the incision, leaving a cavity within the breast.
Typically, pathology is determined after the surgery. A “clean” margin is a pathologic finding indicating there are no cancer cells at the resection margin. After assuring the margin surrounding the cavity is “clean”, a course of radiotherapy is administered to reduce the likelihood of tumor recurrence. Brachytherapy is one modality of such radio-therapy and is of particular interest with this invention. During the brachytherapy treatment planning process, consideration is given to preventing collateral damage to radiation-sensitive structures closely adjacent to the tissue to be irradiated. Such structures may include bone, organs and skin. Where such structures are at risk, the preferred level of radiation therapy for diseased tissue is often moderated to prevent collateral damage, therefore lessening the therapeutic dosage which would otherwise preferably be delivered to target tissues surrounding the cavity.
In instances where such structures exist, and dose moderation is indicated, there is a need for local shielding or attenuation apparatus which can be applied within the cavity adjacent to the at-risk tissues in order effectively to moderate the dose selectively while not detracting from the preferred dosage delivered to diseased tissue elsewhere within the cavity. It is an object of this invention to provide convenient apparatus and methodology to locally moderate brachytherapy radiation.